linux-kernel - Re: [PATCH v1 4/7] iommu/vt-d: Remove unnecessary local variable initializations

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Message-ID: <886e860a-f620-7b12-2611-228adcfa82c8@linux.intel.com>
Date:   Mon, 11 Feb 2019 11:38:43 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     bjorn@...gaas.com
Cc:     baolu.lu@...ux.intel.com, Bjorn Helgaas <helgaas@...nel.org>,
        Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 4/7] iommu/vt-d: Remove unnecessary local variable
 initializations

Hi,

On 2/11/19 11:33 AM, Bjorn Helgaas wrote:
> On Sun, Feb 10, 2019 at 8:00 PM Lu Baolu <baolu.lu@...ux.intel.com> wrote:
>>
>> Hi,
>>
>> On 2/9/19 6:06 AM, Bjorn Helgaas wrote:
>>> From: Bjorn Helgaas <bhelgaas@...gle.com>
>>>
>>> A local variable initialization is a hint that the variable will be used in
>>> an unusual way.  If the initialization is unnecessary, that hint becomes a
>>> distraction.
>>>
>>> Remove unnecessary initializations.  No functional change intended.
>>>
>>> Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
>>> ---
>>>    drivers/iommu/intel-iommu.c |   27 +++++++++++++--------------
>>>    1 file changed, 13 insertions(+), 14 deletions(-)
>>>
>>> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
>>> index 81077803880f..2acd08c82cdc 100644
>>> --- a/drivers/iommu/intel-iommu.c
>>> +++ b/drivers/iommu/intel-iommu.c
>>> @@ -865,7 +865,7 @@ static void free_context_table(struct intel_iommu *iommu)
>>>    static struct dma_pte *pfn_to_dma_pte(struct dmar_domain *domain,
>>>                                      unsigned long pfn, int *target_level)
>>>    {
>>> -     struct dma_pte *parent, *pte = NULL;
>>> +     struct dma_pte *parent, *pte;
>>>        int level = agaw_to_level(domain->agaw);
>>>        int offset;
>>>
>>> @@ -922,7 +922,7 @@ static struct dma_pte *dma_pfn_level_pte(struct dmar_domain *domain,
>>>                                         unsigned long pfn,
>>>                                         int level, int *large_page)
>>>    {
>>> -     struct dma_pte *parent, *pte = NULL;
>>> +     struct dma_pte *parent, *pte;
>>>        int total = agaw_to_level(domain->agaw);
>>>        int offset;
>>>
>>> @@ -954,7 +954,7 @@ static void dma_pte_clear_range(struct dmar_domain *domain,
>>>                                unsigned long start_pfn,
>>>                                unsigned long last_pfn)
>>>    {
>>> -     unsigned int large_page = 1;
>>> +     unsigned int large_page;
>>>        struct dma_pte *first_pte, *pte;
>>>
>>>        BUG_ON(!domain_pfn_supported(domain, start_pfn));
>>> @@ -1132,7 +1132,7 @@ static struct page *domain_unmap(struct dmar_domain *domain,
>>>                                 unsigned long start_pfn,
>>>                                 unsigned long last_pfn)
>>>    {
>>> -     struct page *freelist = NULL;
>>> +     struct page *freelist;
>>
>> I am afraid this change might cause problem. "freelist" might go through
>> dma_pte_clear_level() without any touches.
> 
> Thanks for your review!  Can you clarify your concern?  "freelist"
> isn't passed into dma_pte_clear_level().  Here's the existing code

Oh!

Yes, you are right. I confused it with another function. Sorry about it.

Best regards,
Lu Baolu